1. Field of the Invention
The present invention relates to power conversion technology and more particularly, to a power converter having a relatively higher efficiency at low load.
2. Description of the Related Art
During power conversion of a conventional DC-DC converter, power loss is inevitable. This power loss lowers the conversion efficiency.
However, power density requirement for DC-DC converter is getting critical. The most popularly accepted method to enhance the conversion efficiency of a DC-DC converter is the use of a power MOSFET at the secondary side as a synchronous rectification switch device. This method effectively enhances the efficiency during high load. However, due to increased power loss during driving, this method cannot eliminate no-load power loss, resulting in low efficiency at no-load.
U.S. Pat. No. 7,443,146 discloses a DC-DC converter entitled “Auxiliary turn-on mechanism for reducing conduction loss in body-diode of low side MOSFET of coupled-inductor DC-DC converter”. This design has the aforesaid drawback of no-load conduction loss and the drawback of low efficiency at low load.
Taiwan Patent M374229, issued to the present inventor, discloses a technique that reduces no-load conduction loss. However, this design is based on current detection at the primary side of the transformer. It does not involve the technique for making a decision at the secondary side to reduce standby loss without through the primary side. This prior art design is functional to reduce no-load conduction loss, however, there is still room for improvement.